1. Field of the Invention
The present invention relates to a multilayer plastic composition pipe having an inner layer that has been made lastingly antistatic by addition of graphite fibrils.
2. Discussion of the Background
Multilayer pipes based on polyamides are known (DE-A 41 12 662, 41 12 668, 41 37 430, 41 37 431, 41 37 434, 42 07 125, 42 14 383, 42 15 608, 42 15 609, 42 40 658, 43 02 628, 43 10 884, 43 26 130, 43 36 289, 43 36 290, 43 36 291, 44 10 148, WO-A93/21466, EP-A-0 198 728 and EP-A-0 558 373). Making the inner layer conductive by addition of carbon black or carbon fibers is also know (see DE-A 40 25 301).
However, the use of such conductive inner layers is associated with a series of disadvantages:
a) They are insufficiently resistant to peroxide-containing fuels (sour gas). This shows up, for example, in a serious deterioration of the cold impact toughness occurring after only relatively short storage time in contact with sour-gas-containing fuels (e.g. according to the Ford specification FLTM AZ 105-01, PN 180 or according to the GM specification GM213M, PN 50). PA1 b) After bending, thermoforming or after prolonged contact with fuel, the layers have sharply reduced conductivity, which can lead to complete loss. PA1 c) The surface roughness leads to leakages at connections using conventional Quick Connectors. PA1 d) The high carbon black or fiber loading in the molding compositions results in a high pressure build-up during extrusion. This requires a lowering of the production rate to uneconomically low values. PA1 e) The use of carbon fibers causes an undesired increase in the flexural stiffness. PA1 f) Finally, the conventional amounts of added carbon black undesirably reduce the cold impact toughness. PA1 I. An outer layer comprising a thermoplastic molding composition and PA1 II. An inner layer comprising an electrically conductive thermoplastic molding composition, PA1 (I) an outer layer comprising a thermoplastic molding composition and PA1 (II) an inner layer comprising an electrically conductive thermoplastic molding composition and graphite fibrils.